1. Field of the Invention
The present invention relates generally to a backlighting system especially suitable for use with liquid crystal displays. In particular, it contains certain improved features of a backlighting system of the type disclosed in the above-recited copending application.
2. Description of the Related Art
Liquid crystal displays (LCDs) are commonly used in portable computer systems, televisions, and other electronic display devices. Large area, high performance LCDs require a source of lighting for operation. Backlighting the LCD has become the most popular source of light in personal computers, televisions, as well as projector type displays. In general, there is a need to obtain a sufficiently bright backlighting with as little power consumption as possible. Backlighting systems with a specified degree of collimating, that it is, a limited divergence angle is necessary for such configurations as three cell stacked assembly (TSTN). Since most LCDs have very low transmission and view-angle dependent characteristics, it is sometimes desirable to use more than one light source efficiently for brighter picture presentation. As an example, transmission of a color active matrix LCD is only about 2% and a hot cathode fluorescent lamp, which consumes significantly more energy than a cold cathode fluorescent lamp, is often needed for its back lighting. With the backlighting assembly designed in accordance with the present invention, efficiency in converting light from a linear diffuse light source to a flat display panel, such as LCD, can be significantly improved. This invention can therefore prolong the life time of a battery powering a portable LCD display. Uniformity of the backlighting as well as small space for convenience of portability are also achieved with the present invention.
In most of the existing backlighting systems, the mechanism that brings light out of the light pipe is based on the principal of random scattering which is not only wavelength dependent, but also not very efficient. In addition, this approach can not provide collimated backlighting which is needed for use in applications like stacked liquid crystal displays to avoid parallax effect. Although some approaches have been proposed to obtain collimated backlighting for such displays, they all need a point light source and an optical system based on lenses and mirrors. Since a point light source currently available is generally less power-efficient than a fluorescent lamp and in most cases requires a cooling system such as a fan, and optical systems based on lenses and mirrors which take up a large space, techniques for highly collimated light sources presented before were not practical for the backlighting of portable computers and flat television sets. For this reason, the stacked panel technology is limited to projector type display at this moment.
As will be seen hereinafter, with the backlighting assembly designed in accordance with the present invention, a compact and power-saving light source, which can provide backlighting of both high intensity and controllable collimation, may be applied to stacked panel displays, colored displays in portable computers as well as real time flat displays.